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Abstract
Background: The in vivo correlates of microembolic signals (MES) are still unknown. Platelet-associates (PA) with monocytes or granulocytes or platelet aggregates only may represent these correlates.
Methods: Thirty patients with asymptomatic carotid stenosis >50% and 16 patients with acute (<4 days) atherothrombotic stroke were investigated. PA, P-selectin and thrombospondin expressions on platelets were assessed by flow cytometry. Soluble P-selectin (sPS) levels were assessed. MES detections were performed by transcranial Doppler sonography for 1 hour. PA, P-selectin and thrombospondin expressions on platelets and sPS levels were compared between MES-positive (MES+) and MES-negative (MES−) patients.
Results: Eight patients (27%) with asymptomatic carotid stenosis had 1–26 MES/h. Degree of stenosis was 78 ± 10% in MES− and 88 ± 8% in the MES+ (p=0.01). There were no differences in percentages of PA. P-selectin and thrombospondin surface expression was lower in MES+, but this was not significant. sPS levels were higher in MES+ (122 ± 27 ng/ml versus 80 ± 25 ng/ml in MES−, p=0.01). Seven (44%) patients with stroke had 1–39 MES/h. There were no differences in percentages of PA. MES+ had higher sPS levels (178 ± 43 versus 121 ± 44 ng/ml, p=0.02) and less P-selectin surface expression than MES− (9.0 ± 3.4 versus 4.5 ± 1.6%, p=0.004).
Conclusion: High levels of sPS in MES+ and lower expression of platelet activation markers on platelets' surface suggest shedding of activation markers from the platelets' surface and thus enhanced activation of platelets of MES+ compared with MES−. PA are probably not the clinical correlates of MES, but platelets seem to be the main cellular element of solid cerebral microemboli.